Scientist David Neufeld is searching for evidence of a small molecule called mercapto in interstellar gas. Here, he's inside the SOFIA, a modified 747, while it was parked at Andrews Air Force Base on Sept. 23.

A hatch near the tail of the plane opens to let SOFIA's telescope peer out. The plane-mounted telescope flies above most of the moisture in the Earth's atmosphere, allowing for clearer images than can be captured from ground-based telescopes.

The spike marked in red on this graph from data from a recent SOFIA flight is just what researcher David Neufeld was looking for. It indicates the presence of mercapto radicals, a sulfur-hydrogen molecule, in interstellar gas.

Courtesy of David Neufeld

Astronomers are lining up to use a powerful new NASA telescope called SOFIA. The telescope has unique capabilities for studying things like how stars form and what's in the atmospheres of planets.

But unlike most of the space agency's telescopes, SOFIA isn't in space — it flies around mounted in a Boeing 747 jet with a large door cut on the side so the telescope can see out. Putting a telescope in space makes sense: There's no pesky atmosphere to make stars twinkle. But why put one on a plane?

One reason is that the plane lands every day, says Alycia Weinberg, an astronomer at the Carnegie Institution for Science. She's in charge of planning observations on SOFIA, the Stratospheric Observatory for Infrared Astronomy. Weinberg says those daily landings let researchers fix things or upgrade instruments. With no more space shuttle missions, fixing telescopes in space ranges from nearly impossible to impossible.

Another reason a flying telescope makes sense is that at 45,000 feet, you're above most of the moisture in the atmosphere. For astronomers, that's important, because water vapor makes viewing the sky at infrared wavelengths impossible.

Like sounds that are too low or too high for our ears to hear, infrared wavelengths are light that the human eyeball can't see. But they're there, and Weinberg says lots of things glow at infrared wavelengths like "the cocoons of dust that old stars give off as they go through their final stages of life." Those cocoons of dust are where new stars come from.

One of the things astronomers especially like to do with light from distant objects is put it through a spectrometer. That's an instrument that can reveal the kinds of atoms and molecules that are in the light from whatever the telescope is pointed at. David Neufeld, a professor of physics and astronomy at Johns Hopkins University, has big plans for one of SOFIA's spectrometers.

"I'm looking for a small molecule composed of one sulfur atom and one hydrogen atom," Neufeld says. "It's called mercapto, and it's never been seen before in the interstellar gas."

Neufeld will be observing a cloud of gas in the interstellar space between Earth and a patch of space with the memorable name W49N. The reason Neufeld is interested in mercapto radicals is that they form at certain temperatures.

"So if we see it, what it will tell us is that the clouds of interstellar gas that we are looking at, which are thought to be very, very cold, may have parts of them where it's been heated up to much higher temperatures," he says.

And that information will help explain how new stars form out of these clouds of gas. This is one of those rare times in science when there might actually be a eureka moment. Neufeld says if it's there, mercapto will show up as a line in a readout from the spectrometer.

"[We] may see nothing, the instrument may not work, but hopefully pretty quickly we'll see a hint of the line. So hopefully it will seem like a eureka moment, anyway," he says.

A Delayed Discovery

Neufeld was supposed to board SOFIA at Andrews Air Force Base outside Washington, D.C. It stopped at Andrews on its way from an air show in Germany to its home base in Palmdale, Calif.

That was the plan, anyway, but the night before the flight, the NASA press office called to cancel the trip. John Gegosian said there were two reasons: "First, there's a cooling fan for the telescope that malfunctioned. The second reason was the weather."

It had been raining heavily all week in Washington and the forecast called for more. Flight rules say SOFIA can't take off in a rainstorm because water might get into the telescope's sensitive equipment. So no scientific observations on the way back to Palmdale, and no passengers.

A few days later the fan was fixed, and last Tuesday night SOFIA was able to observe Neufeld's interstellar gas cloud. Neufeld couldn't make it out to California for that flight, so he waited by his computer for an email with the results. It came right after the plane landed Wednesday morning.

"It was immediately obvious that we had an absolutely clear detection of the mercapto radicals, so I was absolutely delighted," he says.

A sort of virtual eureka moment.

Copyright 2011 National Public Radio. To see more, visit http://www.npr.org/.

Transcript

SCOTT SIMON, host: Astronomers are lining up to use a powerful new NASA telescope called SOFIA. Unlike most of the space agency's telescopes, SOFIA isn't actually in space - it flies around mounted in a 747 with a large door cut out one of the sides so the telescope can see out. NASA asked NPR's science correspondence Joe Palca to join astronomers on a trip aboard the new flying observatory, and here's his report.

JOE PALCA: Who could resist a ride in a 747 with a large hole cut in the side? When NASA called I said, sign me up. But I was unclear about something. Putting telescopes in space makes sense. There's no pesky atmosphere to make stars twinkle. But why put a telescope on an airplane? Actually, there are several reasons.

ALYCIA WEINBERG: One is that it lands every day.

PALCA: Alycia Weinberg is an astronomer at the Carnegie Institution for Science. She says because SOFIA lands every day you can fix things or upgrade the instruments. Can't do that with a space telescope anymore. And then there's the advantage of a flying telescope for doing what's called infrared astronomy. And what you ask is infrared astronomy? Well, just as there are sounds that are too low or too high for our ears to hear, there are wavelengths of light that the human eyeball can't see, but they're there. You can't do infrared astronomy on the ground. The water vapor of the atmosphere gets in the way. But at 45,000 feet, you're above most of the moisture in the atmosphere.

Weinberg says there are really interesting things you can only see with an infrared telescope. For example...

WEINBERG: The cocoons of dusts that old stars give off as they go through their final stages of life.

PALCA: Those cocoons of dust are where new stars come from. On my flight, an astronomer named David Neufeld will be looking at the infrared light from an interstellar gas cloud. I decided to toodle up to his office in Baltimore before the flight to talk about his plans, because A, it was going to be noisy on the airplane, and B, he would be busy during the flight. He explained he was looking for a specific molecule in the gas cloud.

DAVID NEUFELD, DEPARTMENT OF PHYSICS AND ASTRONOMY, JOHNS HOPKINS UNIVERSITY: I'm looking for a small molecule composed of one sulfur atom and one hydrogen atom. It's called mercapto, or mercapto radicals, and it's never been seen before in the interstellar gas.

PALCA: The reason Neufeld is interested in mercapto radicals is they only form at certain temperatures.

UNIVERSITY: So if we see it, what it will tell us is that the clouds of interstellar gas that we're looking at, which are traditionally thought to be very, very cold, may have parts of them where it's been heated up to much higher temperatures.

PALCA: Stars are forming the material in these interstellar gas clouds. Finding this sulfur-hydrogen molecule will help explain how get from a gas cloud to a star. This is one of those rare times in science when there might actually be a eureka moment. Neufeld says if it's there, the molecule show up as a specific line in a read-out from one of the instruments attached to the SOFIA telescope.

UNIVERSITY: We may see nothing, the instrument may not work, but hopefully we'll see, you know, pretty quickly we'll see a hint of the line. So hopefully it will seem like a eureka moment, anyway.

(SOUNDBITE OF LAUGHTER)

PALCA: I've always wanted to be present at the moment of discovery so I was looking forward to our upcoming flight. The plan was to meet up again at Andrews Air Force Base just outside of Washington. SOFIA was stopping there on its ways back from an air show in Germany. The telescope is a joint project with the German space agency. SOFIA would observe Neufeld's gas cloud on its way from Andrews back to its home base in Palmdale, California. But, the night before the flight, I got a call. It was the NASA press office. The trip was cancelled. What? Despite the fact it was pouring down with rain, I went out to Andrews and demanded an explanation.

Well, actually, the NASA press office invited me out to Andrews for a tour of the plane as a consolation prize. So, why weren't we flying?

JOHN GAGOSIAN: There were really two reasons. The first reason is there's a cooling fan for the telescope that malfunctioned.

PALCA: John Gagosian is the program executive for SOFIA at NASA headquarters.

GAGOSIAN: The second reason is the weather.

PALCA: Flight rules say SOFIA can't take off in a rain storm, because water might get into the telescope's sensitive equipment. So no scientific observations on the way back to Palmdale, and no passengers. A few days later, the fan was fixed and last Tuesday night, SOFIA got to observe Neufeld's interstellar gas cloud- without Neufeld. He couldn't make the rescheduled flight, and if I was bummed, imagine how he felt. He had to wait for an email with the results. It came right after the plane landed.

UNIVERSITY: It was immediately obvious that we had an absolutely clear detection of the mercapto radicals, so I was really delighted.

PALCA: A sort of a virtual eureka moment. Joe Palca, NPR News. Transcript provided by NPR, Copyright National Public Radio.